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From: Marc Gonzalez <marc.w.gonzalez@free.fr>
To: Walter Wu <walter-zh.wu@mediatek.com>,
	Dmitry Vyukov <dvyukov@google.com>
Cc: LKML <linux-kernel@vger.kernel.org>,
	kasan-dev <kasan-dev@googlegroups.com>,
	Alexander Potapenko <glider@google.com>,
	Matthias Brugger <matthias.bgg@gmail.com>,
	Andrey Ryabinin <aryabinin@virtuozzo.com>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH] kasan: fix the missing underflow in memmove and memcpy with CONFIG_KASAN_GENERIC=y
Date: Mon, 30 Sep 2019 10:57:39 +0200	[thread overview]
Message-ID: <a3a5e118-e6da-8d6d-5073-931653fa2808@free.fr> (raw)
In-Reply-To: <1569818173.17361.19.camel@mtksdccf07>

On 30/09/2019 06:36, Walter Wu wrote:

>  bool check_memory_region(unsigned long addr, size_t size, bool write,
>                                 unsigned long ret_ip)
>  {
> +       if (long(size) < 0) {
> +               kasan_report_invalid_size(src, dest, len, _RET_IP_);
> +               return false;
> +       }
> +
>         return check_memory_region_inline(addr, size, write, ret_ip);
>  }

Is it expected that memcpy/memmove may sometimes (incorrectly) be passed
a negative value? (It would indeed turn up as a "large" size_t)

IMO, casting to long is suspicious.

There seem to be some two implicit assumptions.

1) size >= ULONG_MAX/2 is invalid input
2) casting a size >= ULONG_MAX/2 to long yields a negative value

1) seems reasonable because we can't copy more than half of memory to
the other half of memory. I suppose the constraint could be even tighter,
but it's not clear where to draw the line, especially when considering
32b vs 64b arches.

2) is implementation-defined, and gcc works "as expected" (clang too
probably) https://gcc.gnu.org/onlinedocs/gcc/Integers-implementation.html

A comment might be warranted to explain the rationale.

Regards.

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  reply	other threads:[~2019-09-30  8:57 UTC|newest]

Thread overview: 45+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-09-27  3:43 Walter Wu
2019-09-27 13:07 ` Dmitry Vyukov
2019-09-27 14:22   ` Walter Wu
2019-09-27 19:41     ` Dmitry Vyukov
2019-09-30  4:36       ` Walter Wu
2019-09-30  8:57         ` Marc Gonzalez [this message]
2019-10-01  2:36           ` Walter Wu
2019-10-01  3:01             ` Dmitry Vyukov
2019-10-01  3:18               ` Walter Wu
2019-10-02 12:15         ` Walter Wu
2019-10-02 13:57           ` Dmitry Vyukov
2019-10-03  2:17             ` Walter Wu
2019-10-03  6:26               ` Dmitry Vyukov
2019-10-03  9:38                 ` Walter Wu
2019-10-03 13:51                   ` Walter Wu
2019-10-03 14:53                     ` Dmitry Vyukov
2019-10-04  4:42                       ` Walter Wu
2019-10-04  8:02                         ` Walter Wu
2019-10-04  9:18                           ` Dmitry Vyukov
2019-10-04  9:44                             ` Walter Wu
2019-10-04  9:54                               ` Dmitry Vyukov
2019-10-04 12:05                                 ` Walter Wu
2019-10-04 13:52                                   ` Dmitry Vyukov
2019-10-07  3:22                                     ` Walter Wu
2019-10-07  7:29                                       ` Dmitry Vyukov
2019-10-07  8:18                                         ` Walter Wu
2019-10-07  8:24                                           ` Dmitry Vyukov
2019-10-07  8:51                                             ` Walter Wu
2019-10-07  8:54                                               ` Dmitry Vyukov
2019-10-07  9:03                                                 ` Walter Wu
2019-10-07  9:10                                                   ` Dmitry Vyukov
2019-10-07  9:28                                                     ` Walter Wu
2019-10-07  9:50                                                       ` Walter Wu
2019-10-07 10:51                                                         ` Dmitry Vyukov
2019-10-07 12:03                                                           ` Walter Wu
2019-10-07 12:19                                                             ` Dmitry Vyukov
2019-10-07 12:32                                                               ` Walter Wu
2019-10-07 13:33                                                                 ` Dmitry Vyukov
2019-10-08  6:15                                                                   ` Walter Wu
2019-10-08  9:47                                                                     ` Qian Cai
2019-10-08 11:02                                                                       ` Walter Wu
2019-10-08 11:42                                                                         ` Qian Cai
2019-10-08 12:07                                                                           ` Walter Wu
2019-10-08 12:11                                                                           ` Dmitry Vyukov
2019-10-14  2:19                                                                             ` Walter Wu

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